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Hi all!
New guy to the site. Googling the net for information on the 3.6L LLT engine led me here. With so much confusing information on the web these days, this site seemed to be very informative with its answers ... so here I am! The vast majority of my engine building experience has been with old-school carbureted pushrod operated V8s. So this overhead cam computer controlled LLT V6 is all new to me. I need some help from those that have worked on this engine for a while ... that's where you guys come in!
A little background on my current project. I recently picked up a 2010 Synergy Green Camaro LT with the 3.6L LLT and a 6 speed transmission. The previous owner bought it with a blown engine that ultimately seized. He bought a remanufactured "long block" from Advanced Auto Parts and built by Spartan Engines of Texas for them. He took the remanufactured long block and the car to a shop where they pulled the blown engine, swapped the necessary components over to the new long block and then reinstalled it into the car. Previous owner stated that the car ran fine for the first 19 miles and then started to run like crap. He took it to a different shop, and they discovered that it had bent a #3 exhaust valve and tossed a rocker arm. Previous owner got into a big pissing match with Advanced Auto Parts and the shop that installed the motor with each blaming the other for the engine failing after only 19 miles. After getting nowhere with Advanced Auto Parts and the installation shop, the frustrated previous owner decided to wash his hands of the whole mess and put it up for sale. This is where I came in. It has a little over 100K on it and a sick motor, but the Synergy Green and the price was too much for me to resist. So I bought it and am now doing "forensics" on it trying to figure out what happened to the engine.
I pulled the engine and completely disassembled it down to the bare block. Here is what I found. As stated, the #3 engine bent an exhaust valve for some reason? When it bent, it wouldn't fully close and that created enough slack for the rocker arm to pop off. But why did the valve bend? Camshaft timing was perfect. There is no evidence of the cam timing being incorrect or of the valves hitting the pistons. I could not find any evidence of any foreign object being in the combustion chamber and jamming the valve. The surfaces of the pistons, valves and combustion chambers are clean and damage free. Oddly, I did find a small bit of oil on top of the #3 piston. The cylinder, combustion chamber, valves and spark plug all had a fine layer of oil on them. Perhaps since this cylinder wasn't firing (due to the massive compression leak through the bent valve) there wasn't any combustion pressure on the rings allowing some oil to slip by? I removed the piston to check for ring damage and found none. Oddly this engine has two pice oil rings (instead of the traditional three piece) oil rings installed - a spiral oil spring inside of a one piece u-shaped tension ring (never have seen one like that before)? All of the other five cylinders and pistons looked okay and like they had been firing, although a little on the rich side (perhaps trying to compensate for the badly misfiring #3?).
Searching for something, I finally found a potential culprit in the intake plenum. When the original engine blew and seized, it apparently had a catastrophic piston failure. Very small parts of the failed piston blew back up the intake runner and collected inside of the intake plenum. Apparently the installation shop never bothered to look inside of the plenum. They just removed it from the blown engine and transferred it to the new one. I theorized that it may have been possible for a piece of the failed piston inside of the plenum may have been sucked into the #3 cylinder and somehow got jammed in there bending the valve. However, as I said before, I could find no physical damage to the piston, valve face, valve seat or combustion chamber. I would think that if a piece large enough to bend a valve got in there, it would have left some telltale evidence in the form of nicking or gouging the surfaces in there? So even though my theory is plausible, I don't think that is what happened.
I'm really stumped on this one. I can't figure out what caused just that one valve to bend and then left no evidence other than the bent valve itself? I was really hoping to find the "smoking gun" before I start to put this engine back together. Maybe it was just a cheap quality valve used by Spartan Engines? Excessive valve guide clearance allowing the valve to "wander" on the seat? I just don't know at this point.
So, if any of you experienced 3.6L LLT engine builders out there have any insight as to what may have happened, I would sure like to hear from you! Thanks in advance for your time and help!
Cheers,
Tom
New guy to the site. Googling the net for information on the 3.6L LLT engine led me here. With so much confusing information on the web these days, this site seemed to be very informative with its answers ... so here I am! The vast majority of my engine building experience has been with old-school carbureted pushrod operated V8s. So this overhead cam computer controlled LLT V6 is all new to me. I need some help from those that have worked on this engine for a while ... that's where you guys come in!
A little background on my current project. I recently picked up a 2010 Synergy Green Camaro LT with the 3.6L LLT and a 6 speed transmission. The previous owner bought it with a blown engine that ultimately seized. He bought a remanufactured "long block" from Advanced Auto Parts and built by Spartan Engines of Texas for them. He took the remanufactured long block and the car to a shop where they pulled the blown engine, swapped the necessary components over to the new long block and then reinstalled it into the car. Previous owner stated that the car ran fine for the first 19 miles and then started to run like crap. He took it to a different shop, and they discovered that it had bent a #3 exhaust valve and tossed a rocker arm. Previous owner got into a big pissing match with Advanced Auto Parts and the shop that installed the motor with each blaming the other for the engine failing after only 19 miles. After getting nowhere with Advanced Auto Parts and the installation shop, the frustrated previous owner decided to wash his hands of the whole mess and put it up for sale. This is where I came in. It has a little over 100K on it and a sick motor, but the Synergy Green and the price was too much for me to resist. So I bought it and am now doing "forensics" on it trying to figure out what happened to the engine.
I pulled the engine and completely disassembled it down to the bare block. Here is what I found. As stated, the #3 engine bent an exhaust valve for some reason? When it bent, it wouldn't fully close and that created enough slack for the rocker arm to pop off. But why did the valve bend? Camshaft timing was perfect. There is no evidence of the cam timing being incorrect or of the valves hitting the pistons. I could not find any evidence of any foreign object being in the combustion chamber and jamming the valve. The surfaces of the pistons, valves and combustion chambers are clean and damage free. Oddly, I did find a small bit of oil on top of the #3 piston. The cylinder, combustion chamber, valves and spark plug all had a fine layer of oil on them. Perhaps since this cylinder wasn't firing (due to the massive compression leak through the bent valve) there wasn't any combustion pressure on the rings allowing some oil to slip by? I removed the piston to check for ring damage and found none. Oddly this engine has two pice oil rings (instead of the traditional three piece) oil rings installed - a spiral oil spring inside of a one piece u-shaped tension ring (never have seen one like that before)? All of the other five cylinders and pistons looked okay and like they had been firing, although a little on the rich side (perhaps trying to compensate for the badly misfiring #3?).
Searching for something, I finally found a potential culprit in the intake plenum. When the original engine blew and seized, it apparently had a catastrophic piston failure. Very small parts of the failed piston blew back up the intake runner and collected inside of the intake plenum. Apparently the installation shop never bothered to look inside of the plenum. They just removed it from the blown engine and transferred it to the new one. I theorized that it may have been possible for a piece of the failed piston inside of the plenum may have been sucked into the #3 cylinder and somehow got jammed in there bending the valve. However, as I said before, I could find no physical damage to the piston, valve face, valve seat or combustion chamber. I would think that if a piece large enough to bend a valve got in there, it would have left some telltale evidence in the form of nicking or gouging the surfaces in there? So even though my theory is plausible, I don't think that is what happened.
I'm really stumped on this one. I can't figure out what caused just that one valve to bend and then left no evidence other than the bent valve itself? I was really hoping to find the "smoking gun" before I start to put this engine back together. Maybe it was just a cheap quality valve used by Spartan Engines? Excessive valve guide clearance allowing the valve to "wander" on the seat? I just don't know at this point.
So, if any of you experienced 3.6L LLT engine builders out there have any insight as to what may have happened, I would sure like to hear from you! Thanks in advance for your time and help!
Cheers,
Tom
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